diff --git a/src/cyxtrax/io/save_map.py b/src/cyxtrax/io/save_map.py
index 2329034c3e0ffb59d64ef437e0937068ad7453b6..00d685cca9eb3881f9557321691424c4a92733f9 100644
--- a/src/cyxtrax/io/save_map.py
+++ b/src/cyxtrax/io/save_map.py
@@ -17,7 +17,7 @@ def save_atlas(
     save_folder: Path,
 ):
     save_path = save_folder / f"{atlas_name}.h5"
-    file = h5py.File(save_path, "a")
+    file = h5py.File(save_path, "w")
 
     x_px = maps.shape[0]
     y_px = maps.shape[1]